IN 1971, IN THE CENTERFOLD of their live album "Skull & Roses," the Grateful Dead shouted out to their growing legion of fans, "Dead Freaks Unite."

"Who are you? Where are you? How are You?" they wanted to know, and directed correspondence to P.O. Box 1065, San Rafael, the band's mailing address for the next 35 years.

That triggered a first salvo of letters containing, among other things, poetry, autograph requests, marriage proposals, a death threat or two, spaced-out hippie ramblings and the occasional mind-blowing piece of art work.

Some of the more artistic missives were featured in "The Official Book of the Dead Heads," a 1983 compendium by Paul Grushkin consisting of bumper stickers, posters, tickets, backstage passes and other band-related memorabilia.

"For about two years I looked at every newspaper clipping and every letter, everything that had been saved following the 'Dead Freaks Unite' message in 1971," the now 60-year-old author recalled.

Then a young Stanford grad, Grushkin endeared himself to the band's office staff by volunteering to help them read the rising flood of fan mail.

Now, after a 25-year career in rock merchandising, he's authored a sequel, "Dead Letters: The Very Best Grateful Dead Fan Mail" (Voyager Press, $29.99), a glossy hardcover (and e-edition) packed with more than 500 hand-drawn and colored envelopes from Deadheads who were competing for coveted concert tickets.

Trying to stand out in the avalanche of mail order requests after the band formed its own ticketing service in 1983, Deadheads began decorating No. 10-size envelopes with all manner of psychedelic art.

"Sometime in the first six months after the band began mail order, an unknown Deadhead decided that if he decorated the outside of the envelope, it would catch the attention of the people issuing the tickets," Grushkin explained. "And that spread like wildfire."

These mail-order masterpieces included portraits of favorite band members, often Jerry Garcia, Phil Lesh and Bob Weir, impressionistic renderings of song lyrics and creative interpretations of the band's famed iconography — skulls and skeletons, bears and terrapins, tie-dye, flying eyeballs and one of the most instantly recognizable logos in rock 'n' roll, the skull and lightning bolt affectionately known as "the Stealie."

"I don't think there is another band in history that had a fandom that would have gone to this extent," Grushkin said. "You're talking about people who could be truck drivers, bakers, homemakers, professors, chemists, you name it. It reaffirmed to me that this is one dedicated fandom."

The letters hit critical mass after the Dead scored their one and only commercial hit, "Touch of Grey," in 1987. After that, attendance at their concerts tripled, making them among the top five touring acts in the world. For an average show, the band's P.O. Box would overflow with 60,000 requests for 10,000 available tickets.

"The ticket staff would go to the San Rafael post office and pick up 80 trays of mail filled with a million dollars worth of mail-order coupons," Grushkin recalled. "The staff would look at all this and try to select who would be lucky enough to go."

This went on for a dozen years, until Garcia's death in 1995, when the band stopped touring as the Grateful Dead.

"For the first 10 years, the most outrageous decorations would indeed catch the eye of the folks on the other end," Grushkin said. "And then you might as well have put all the envelopes on a wall and thrown darts at them and it would have accomplished the same thing, because everybody was decorating. It was like this incredible insiders' competition. We did the math and we figured that close to 10 million envelopes were received by Grateful Dead ticket sales over 12 years."

In 2008, 15,000 of those decorated ticket-request envelopes were donated to the University of Santa Cruz, where they are part of the band's voluminous archives.

Grushkin considered 13,000 for the book, breaking them down into 14 thematic categories and ultimately selecting 550 winners.

"I was dazed by the end," he admitted. "It was this incredible reductive exercise. I had to decide in my mind what art work truly reflected the soul of the Grateful Dead."

In the book's foreword, the world's tallest Deadhead, basketball great Bill Walton, writes, "In the all-encompassing sensations that consume us, never discount the power of the visual...to convey our undying love, admiration, respect, appreciation, gratitude and need to belong."

As a rock historian, Grushkin throws in little-known factoids and memorabilia, including the psychedelic-lettered invitation to the Dead's legendary "afternoon of inter-galactic travel" party at Novato's Rancho Olompali in 1966. He dedicated the book to Eileen Law, aka the "Head Dead Head," the staffer who had the good sense to save the best letters, storing them in an office closet.

For Grushkin, writing "Dead Letters" reaffirmed what he already knew. "People really loved that band," he said. "And they still do."